1. Field of the Invention
The present invention pertains to high explosive, directed energy warheads, more particularly to fragmentation warheads, and most particularly to fragmentation warheads wherein the fragments are comprised of segmented circular rods helically positioned around a cylindrical high explosive charge that provide, upon detonation of the explosive, a continuous, spiral killing mechanism consisting of adjacent and interrelated circular rod segments.
2. Description of the Related Art
The basic function of any weapon is to deliver a destructive force on an enemy target. High explosive warheads cause damage by concussion (blast effects) or by penetration of high-energy fragments. In general, there are three types of high explosive warheads that employ the latter method to accelerate metal fragments generally including (1) directed energy warheads, (2) fragmentation warheads, and (3) continuous-rod warheads (CRW).
Directed Energy Warheads, as used herein, refers to Shaped Charge Warheads and Explosively Formed (a.k.a. forged) Penetrators (EFPs) that are said to be directed in that the high explosive energy is focused on a liner, which is typically made of metal. These warheads consist of a hollow liner of thin metal material backed on the convex side by explosive. Upon detonation, a detonation wave sweeps forward and hydrodynamically collapses the liner (in the case of a shaped charge) or deforms the liner (in the case of EFPs) along its axis of symmetry forming a directed jet or EFP which penetrates a localized area on a target of interest.
The directed energy effects concept can be used in multiples, where metal liners/projectiles are distributed, around the circumference of a high explosive charge. In this case, the detonation does not collapse a liner along its linear axis of symmetry, rather, the detonation wave hits the liners perpendicularly (almost symmetrically to the axis of the liners).
High explosive fragmentation warheads constitute one of the most widely used warhead approaches in all types of ammunition. Fragmentation warheads are intended to defeat virtually all types of targets, excluding overburden targets underground and underwater, and heavily armored targets.
In fragmentation warheads, the detonation of the secondary high explosive core generates a large amount of heat and gaseous products. High explosives have an extremely high rate of reaction and the presence of a detonation (shock) wave that moves faster than the speed of sound in the explosive material. Upon detonation, the metal warhead casing almost instantaneously catastrophically fails and bursts, producing a blast of rapidly expanding hot gases and casing fragments.
The rapidly expanding gasses will compress the surrounding air and create a shock wave which propagates outwards at near the speed of sound in air (˜340 m/s). The energy of the fragments dissipate more slowly than the energy of a shock wave and, thus, fragments tend to be lethal to a greater range than the blast effects for hard targets.
As a function of design, fragments from a fragmenting warhead have various distribution patterns and lethality characteristics. The fragment distribution pattern is a function of the amount and nature of the explosive material (i.e. how energetic the explosion is), the mass of the fragmenting material, the fragmentation size, and the configuration (geometry, initiation scheme) of the warhead. For example, the detonation of a bomb projects the fragments in an approximate cylindrical pattern and a hand-grenade projects fragments in an approximate spherical pattern.
Uncontrolled fragmentation patterns, such as those used in general-purpose bombs, occur by the natural break up of the outer casing occurring from the detonation of the surrounding explosive charge. This event forms fragments of random size and lethality.
Manipulating the fragment formation process can more predictably control fragmentation patterns and fragment uniformity. Controlled fragment formation can be accomplished in several ways including: designing pre-scored failure regions (grid patterns) on the outer/inner casing or outer surface of the explosive; sandwiching an intermediate mesh material between the outer casing and the explosive core; and, arranging preformed fragments around the main charge explosive such as spheres or cubes.
By controlling the fragment formation process, the relative size and, therefore, the optimized bulk fragment distribution pattern over an area is constrained to maximize the defeat probability/lethality against an anticipated target set of known thickness, obliquity, and material properties.
CRW technology incorporates two overlapping layers of ductile rods that are oriented around the circumference running parallel along the length of an explosive core. The rods are alternately connected together, end-to-end, by a weld (in a zigzag/accordion pleat fashion). Upon detonation, the continuous-rod payload rapidly expands radially outward, bending or “unfolding” the welded ends to form a ring of interconnected rods. A ring of interconnected rods is produced about the axis of the weapon. The ring expands from a highly compressed zigzag pattern to an expanded, almost flat, zigzag pattern using an expansion mechanism similar to a half-plane pantograph. During this expansion, the explosive energy is focused in a single plane such that when the rods strike a target, damage is produced by a cutting action giving it the nickname “flying buzzsaw”. The metal density of a normal fragmentation warhead attenuates inversely with the square of the distance (1/R2). However, because it is non-isotropic, the metal density of a continuous-rod payload attenuates inversely as the distance from the point of detonation (1/R). To ensure that the rods stay connected at detonation, the maximum initial rod velocity is limited to the range of 1050 to 1150 meters per second. The initial fragment velocities of fragmentation warheads are in the range of 1800 to 2100 meters per second. Thus, in comparison, CRWs cannot produce as much destructive energy potential as fragmentation warheads. However, the distribution pattern is highly focused, and the rods are interconnected, to increase the relative mass interacting with a target in a highly localized area.
Only one invention known to applicants uses discrete rods in a fragmentation type of warhead and it closely mimics the physical architecture of the CRW (layers of rods that are oriented around the circumference and run parallel and along the length of an explosive core), but without physical interconnections being established between adjacent rods. U.S. Pat. No. 4,216,720 entitled Rod-fragment controlled-motion warhead (RFCMW) discloses destructive fragments used in a warhead that are in the form of discrete tapered rods that are substantially the same length as the cylindrical warhead itself and are placed vertically around and parallel to the axis of the warhead. The warhead system is designed to dynamically rotate the rods to form the expansion and kill radius/mechanism. U.S. Pat. No. 4,216,720 points to some deficiencies of the RFCMW concept as follows: the pattern of these rod-type fragments has been of such a discontinuous nature to results in a high likelihood of missing targets; and, the rods tend to spread in the axial direction, rather than being driven radially.
Another major shortfall of the RFCMW concept is that a high explosive detonation event is used to form the geometric orientation of the rods through a dynamically controlled rotation of each discrete rod to provide the expansion mechanism. The propelling motion is empirically derived for each configuration and optimized to a 90 degree rotation for each discrete rod. If the collective interrelated system of discrete rods under or over rotates, the effective continuous coverage (end-to-end) radius is reduced.
Additionally, the propellering motion of each rod within the RFCMW must have the same angular velocity (and acceleration rate) to ensure the discrete rods do not rotate into each other. The propellering motion of the discrete taper rods requires a perfectly balance rod after that rod has experience some degree of deformation following the explosive detonation of the explosive core. The detonation of the explosive charge will most likely cause spalling and material deformation of the tapered rods, which will randomly change their aerodynamic characteristics while unpredictably shifting the center-of-balance and, thus, introducing random discontinuities in the propellering motion of each discrete rod. If a single rod does not perform as designed or if one discrete rod prematurely encounters an obstacle (such as topography, a tree, etc.) before reaching the target, its rotation will be significantly altered and cause a domino effect whereby the interrelated discrete rods tumble into each other and consume the effective warhead energy.
A further major shortfall in the RFCMW is the aerodynamic stability of this concept whereby the end effect must be achieved by a highly controlled formation pattern that is achieved by dynamic, balanced rotation that is highly intolerant of drift, asymmetries, and induce asymmetries such as spalling and material deformation following the warhead detonation. Time sequencing of six degrees-of-freedom motion must be achieved to propel the discrete rods radially outward, while they are simultaneously and dynamically rotating about their respective precise center axes. This requires that each discrete rod rotates at the same angular rate while experiencing a uniform velocity ratio (uniform velocity to mass ratio) during and after an explosive event across the entire length of the discrete rod which has an unusually high aspect ratio (the claimed length-to-diameter ratio is 28:1) so that all portions are subjected to both the same an outward and angular velocity to arrive at an end-to-end disposition.
Other shortfalls of the RFCMW concept are as follows: the tapered rods will reduce the penetration capability at the thinned portion of the rods and therefore reduce the damage level to the intended target; and, it is doubtful that the warhead is relatively inexpensive as claimed—the warhead would be relatively expensive due to the understanding that the RFCMW requires relatively high control of rod material properties, highly toleranced machined metal parts, manufactured parts, and fabricated assemblies, and a potentially complex explosive initiation system to ensure effective results (also true for a CRW).
Therefore, it is desired to provide a radially expanding kill effect similar to the CRW by using geometrically prearranged segmented circular rods placed horizontally (perpendicular to the warhead axis) around a cylindrical warhead to produce a geometrically coupled, helical spirally ring of interrelated and adjacent segmented circular rods upon detonation of the explosive core, to increase the effective mass on the target within a localized region, to create multiple impact sites within a projected height, to create lethality at and somewhat beyond the full expansion diameter of the warhead, and to create unique target defeat mechanisms compared to that of the CRW or that of all known prearranged fragmentation warheads.